The present invention relates to filament-wound pressure vessels and, in particular, to the formation of pressure vessels having differently-sized polar end openings.
Filament wound pressure vessels are rather widely used and their fabrication fully discussed in a number of prior art patents. In particular, U.S. Pat. No. 3,083,864, issued Apr. 2, 1963 to R. E. Young discloses a vessel similar to present vessel and it also discloses the winding technique used in its fabrication. As there shown, the vessel is an elongate structure, having a cylindrical body portion and symmetrical ovaloid ends which usually are referred to as polar ends. The entire structure is filament wound, or in other words, formed of a continuously wound filamentary material which, for example, may be provided by a graphite fiber winding or the like that is passed at a constant helical winding angle across the ends and length of the vessel. One significant aspect of these vessels is that maximum strength and maximum fiber-utilization efficiency best are achieved by maintaining a winding path which follows the geodesic lines of the particular arcuate surface to be formed. A geodesic line, by common definition is the shortest line between two points on a mathematically derived surface. For example, a geodesic line on a sphere is a well known arc of a great circle.
To achieve the geodesic path, the windings which form the vessel must follow a constant helical winding angle. If the design of the vessel is symmetrical, the constancy of the winding angle presents no particular difficulty. However, if the design includes unsymmetrical areas, the winding angle then must be deviated and, since the line or path then becomes nongeodesic, the strength of the vessel or, in other words, its ability to resist tension forces, is reduced. As a result, additional fibers or the like then must be added to supplement the vessel's strength.
The present invention is concerned primarily with winding angle problems which arise principally when the vessel design criteria involves some lack of symmetry. In this regard, it is known that an inherent feature of a filament wound vessel is the formation of the so-called polar openings, one at each end of the vessels. In many vessels, these polar openings are identical in size so that their presence does not affect symmetry. However, in some vessels such as those intended for use as rocket motor chambers, the design frequently requires that the openings be of a widely varied size to accommodate, for example, the rocket motor nozzle at one end and an igniter at the other. Consequently, when winding rocket motor chambers with which the present invention is primarily concerned, the openings, which conventionally are formed during the winding process, involve a lack of symmetry so that the winding angle must be deviated rather than remain constant. Such a deviation, as stated, results in more helical windings on some parts of the chamber than are required and these added windings increase the overall weight of the chamber. Weight, of course, is a critical parameter in the performance of such aeronautical vehicles so that the increase obviously is undesirable. Even so, customary practice has accepted the added weight even at the expense of the performance as well as the cost factors entailed in the use of additional expensive materials.
It is therefore an object of the present invention to form a filament wound pressure vessel of a type having different sized end openings in a manner that achieves maximum strength to weight efficiency.
More specifically, an object is to provide a pressure vessel in which the filament winding angle is maintained at a constant throughout the length of the chamber.
A further object is to provide a composite filament-wound cylindrical pressure cylindrical vessel specifically adapted for use as a rocket motor chamber having polar end openings of different sizes.
Yet another object is to reduce the weight and improve the performance of rocket motors by improving efficiency of the wound structure of the rocket motor chamber.
Other objects and their attendant advantages will become more apparent in the ensuing description.
Generally considered the present invention utilizes a series of fabrication steps in forming the desired pressure level. First, a filament wound vessel having polar end openings of the same diameter is formed using a constant winding angle permitted by the symmetry of the structure. The precise diameter of the openings is a matter of choice although it should be no larger than the minimum diameter dictated by the design criteria. Finally, the end openings are machined to the larger diameter required by the design. In the machining the filament fibers are cut and weakened in the area of the opening. This area, however, is reinforced by interspersed helically wound mats of wafers. Interspersing of the mats preferably is accomplished in the winding process during which several layers of filaments are provided and the mats are bound between the layers during the winding process.